


Hot Mama

by poubelle_squelette



Category: Undertale (Video Game)
Genre: Alternate Universe - Underswap (Undertale), Blow Jobs, Breeding, Established Relationship, F/M, Hand Jobs, Love Confessions, Monster Heat, Reader Is Not Frisk (Undertale), Reader-Insert, Underswap Sans (Undertale), Vaginal Fingering, Vaginal Sex, reader is female
Language: English
Status: Completed
Published: 2018-09-15
Updated: 2018-09-15
Packaged: 2019-07-12 19:27:09
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,978
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16001741
Author URL: https://archiveofourown.org/users/poubelle_squelette/pseuds/poubelle_squelette
Summary: You just wanted to surprise Blue with a trip to the beach when his annoying brother stopped you at the door."You Really Don’t Want To See Blue Right Now.”"And why is that, exactly?"He pinched his nasal bone. A dim orange glow speckled his face. “Ever Hear Of Heat?”





	Hot Mama

**Author's Note:**

> Ayyyy. So this is a quick one shot. Not really into most monster heat fics because they don't align with my headcanon, but this was pretty fun to write anyway. It takes place in the same universe as my SMT chapter (which is why they go by Blue and Orange), but you don't really need to read that to understand this.

You came up to Blue’s door and knocked several times in succession. You readjusted your hair and waited patiently. Today you were planning on taking him to the beach, something he had mentioned several times over the last month. The rainy season finally let up, so you were going to surprise him.

However, when the door opened, it wasn’t your precious Blue there to greet you, even though you were certain you told him you were coming. Instead it was his younger brother…Kiwi? Shoot, you could never remember his name. But, yeah, sure. Kiwi. He had a backpack slung over his shoulder.

“Heya, Howzit Going?” he asked, leaning against the doorframe.

“Fine,” you said, looking at your shoes. “I didn’t realize you were still in school,” you added, nodding towards the backpack.

He gave it half a glance before saying, “I’m Stayin With Undyne For The Week. You Should Go Home, By The Way.”

You crossed your arms. “Blue and I had plans. I’m taking him to the beach.”

Kiwi snorted. “Yeah, You Aren’t Taking Him Anywhere.”

“Are you planning on stopping me? I didn’t realize he needed to get your permission,” you said defensively. “He’s been talking about it nonstop for the last month, I would hate to break a promise.”

You made a move to go inside, but Kiwi stopped you by blocking the doorway with his arm. “Trust Me. Listen, I Know We Don’t Get Along, But I’m Saying This For Your Sake. You Really Don’t Want To See Blue Right Now.”

You took a deep breath. “Okay, why wouldn’t I want to see my boyfriend, exactly?”

He pinched his nasal bone. A dim orange glow speckled his face. “Ever Hear Of Heat?”

“Yeah, but…OH!”

There was hardly anything known about Monster Heat except that it only happened for a week once every couple of years. You pictured it as being somewhat similar to animals being in heat, since that was your only point of reference. You squirmed a bit. It was kind of a turn on to imagine him hot and bothered and so, so needy. Blue was already pretty insatiable as it was. What would that be like when he wasn’t holding back for you? You licked your lips at the thought. Oh yeah, you were so going to get into that house.

“Listen, I Get That You Like My Bro, But Stay Away,” he said, before closing the door and locking it behind him. He placed a cigarette in his mouth and taped on a pair of sunglasses before hopping in his car. 

You stayed on their porch until Kiwi Whats-his-Face drove away. Fucking finally. You lifted the doormat and using a marble you solved the maze underneath, popping open a secret compartment from the siding of the house. Inside the compartment was a Tetris like building puzzle that needed to be formed into a rectangle that would open and inside was a key. It was a weird mix of puzzles and magic and you just wished they would hide their key in a flower pot like everyone else.

The house was very quiet. You kicked off your shoes and put your bag down by the front door. Blue would probably be in his room, so you hurried down the hall towards his bedroom door. You could hear him moaning inside already. As quietly as you possibly could, you turned the knob. The door creaked open and you stepped inside, closing it with a soft _click!_ The room was already pretty warm and the air was slightly humid and smelled like sweat. 

The first thing you noticed was Blue humping a pillow naked (Blue was naked, the pillow was still modestly covered). He was so focused on that task he hadn’t even noticed that you walked in.

The second thing you noticed was that there was cum absolutely _drenching_ Blue’s bedsheets. Your breath hitched slightly. How many orgasms has he already had? Blue was completely hazy-eyed as he shuddered and collapsed atop the pillow. Whatever the number was just increased by another.

“Hey baby, wouldn’t you much rather be humping something that could hump you back?” you asked. 

Blue locked eyes with you. For a moment, you thought he was going to pounce on you, but instead he broke out in a happy giggle, eyelights popping into stars. “i can’t believe you’re here! papy said you couldn’t come.”

“Well, I suppose he’s right. I couldn’t come…without your help,” you said, unbuttoning your shorts. “So whaddya say?” You pulled your shorts off and tossed them aside. “You want to make your girl very, very happy today?”

Blue hadn’t been able to take his eyes off you since you spoke. He was currently letting his eyes wander up and down your body. “wowzers,” he finally breathed out. “i…hahh,” he let out a long whine and reached down to stroke his painfully hard cock. “sorry i c-can’t, i’m…hnn. it'd be irresponsible and i c-couldn’t do that to you.”

You raised an eyebrow. “You’re worried because of your heat, huh? It’s alright, your bro told me. You don’t need to worry about me Blue. I find your heat… _pretty hot_.”

“fuck,” Blue swore, “stop punning, it’s too much of a turn on.”

You giggled. “I can tell you’re trying to hold back, you’re shaking. Probably _dying_ to get your little bony hands all over me.” You took off your shirt, throwing it aside along with your shorts. “I’m a big girl, I can handle it.”

Blue shuddered, still breathing heavily. “hypotenuse?”

“Because it’s the opposite of right, I remember,” you said. “Don’t worry, I’ll use the safe word if I need to, but I’m not exactly planning on it. So…?”

“i need you so bad,” he whimpered.

“Then come take me, big boy.”

Blue practically leapt off the bed to run towards you. You didn’t even get the chance to properly lean down to kiss him because his hands were already forcefully pulling your face towards his mouth. He deepened the kiss immediately, desperately pushing his tongue between your lips to gain access to the inside of your mouth. You followed his lead, letting him explore your mouth while you reached forward to gently rub his ribs.

Blue broke the kiss and murmured, “harder.”

You strengthened your grip and pulled again. Blue groaned against your mouth, so you continued, paying special attention to the underside of his ribs. Blue took his hands away from your face and moved to your back to unclasp your bra, fingers trembling. You briefly broke your grip to let the bra fall off your arms before returning to your strokes, allowing your fingernails to graze the edges of the bone. 

Blue placed one hand on the back of your head and laced his fingers through your hair while the other dipped into your underwear. He circled your clit before tracing the outline of your entrance. He dragged the slickness back up your slit before finally pushing two fingers in. You clenched around them as he pumped into you. 

“sh-shit,” Blue hissed as a rope of sticky blue cum spurt out onto your thigh. “sorry, sorry.”

You laughed. “It’s okay, Blue. I don’t mind some cum on me.”

“no,” Blue said. “i'm sorry that that’s one less time i’m gonna get to finish in you.”

You swallowed. “How many times did you plan on that, hmm?”

In one swift motion, Blue removed his fingers from you and pulled down your panties. “as many as it takes to fill you until you burst.” 

Without another word, Blue lifted you up over his shoulder. As he carried you back to the bed, his fingers were already back to rubbing your clit. Pressure was already beginning to coil as you squirmed under his grip. He tossed you onto his plush bed and climbed on top of you, pressing his kneecap against you. He grabbed ahold of your legs and let them rest on his shoulders. One of his hands trailed down your leg towards your hip and the other was stroking his cock again. Blue leaned forward and guided his tip towards your folds and pushed himself all the way in.

You yelped from being filled so suddenly, but Blue was already thrusting at an erratic pace. You grabbed the sides of his pubis and dug your nails in, scratching the surface ever so slightly. Blue moaned and held your jaw in place as he once again dove his tongue right into your mouth. You closed your eyes and let your tongue swirl around his. It was an incredibly sloppy kiss, completely lacking in finesse, but it was warm and wet and _hot_ as your saliva mixed with his and you felt his desperation.

Blue pounded into you, knocking the headboard back into the wall in the process. Sweat dripped down his forehead as he pushed harder, lifting your ass up slightly. He cupped your cheeks and gave them a firm squeeze. Now that your hips were higher, he had more leverage to go deeper.

You let out a long whine. “Ahhhh, Blue, fuck. This feels so good.”

“hnn, ah, say that again.”

“This feels so goo-ah!” Blue cut you off by biting a sensitive spot on your neck. He licked the spot and then bit it a second time, lingering and nibbling there. You turned your head so he would have better access to pepper your neck with love bites.

As he nibbled your neck, you pressed your thumbs into his pubis, twisting them around a particularly sensitive spot near the front. Blue bit down on your neck again, harder this time. You felt his hot breath on your skin, panting as he swirled his tongue around that spot a second time. 

Blue’s bones started clacking so you knew he was getting close again. “Fuck, Blue you’re perfect,” you whispered. “So amazing and you make me feel so good. Just fill me up with your cum until you can’t anymore. Fill up every part of me if you have to, I can take it. I can take it all, baby.”

You thought you might’ve been overdoing it, but Blue was shuddering again and a warm, sticky liquid gushed out of him, filling you, with some trickling down your inner thigh. It left an incredibly tingly feeling behind. He smiled and gave you a quick forehead smooch.

Blue was still hard and hadn’t removed himself from you yet, but he did ease up on the pace. He was straining to show self-control, more for your sake than his. 

“I can take it,” you repeated.

Blue studied your face for a minute before nodding and thrusting into you, forgoing any sense of delicacy. You bit your lip as he started rubbing against your clit. You sighed and Blue took that as an opportunity to push his fingers into your mouth. You sucked on his fingers as he rubbed your clit back and forth, picking up a pace to match his thrusts. You bucked up into his hand, which resulted in his fingers getting pushed back further into your mouth. 

You were starting to shake in anticipation as the pleasure continued to build. Blue put more pressure on your clit as he circled it. You whimpered as his cock pumped in and out of you in time with his fingering. Drool began escaping from your mouth, falling along your jawline and onto the pillow. Your vision started going blurry as you focused in on the tingling sensation from Blue’s existing cum.

“you’re gonna take so much of me,” Blue mumbled, “i’ll…i’ll pump so much into you, you’ll be drenched in it. in me.” 

Too many things were stimulating you now. You squeezed your eyes shut and rolled your hips as much as you could in this position. You panted as beads of sweat ran down your own face. Blue pulled out ever so slightly before pushing himself back in at full length. You cried out as you peaked, clenching tightly around his dick. He lurched forward too, unleashing another load into you, cum spilling out and recoating your thighs and dribbling down your ass.

Blue released your legs from his shoulders, letting them rest on the mattress. He continued to rut into you, not slowing down, but suddenly looking much more bashful. “i…um…” He looked away from you, face turning a pale blue. “i…d-do you mind playing along?”

You furrowed your eyebrows and gently removed Blue’s hand from your mouth so you could respond. “Of course I don’t mind. I thought I already was.”

His blush darkened. “y-yeah but…h-heat makes me…territorial. and…um…i…”

You cut him off with a kiss on his hand. “Do what you gotta do. Say what you gotta say. Fuck me however you need. Trust me, I’m following your lead on this. And don’t you dare stop yourself for me again unless I say our safe word, got it?”

Blue’s pupils shifted into stars as he nodded. He pulled his cock out from your soaked pussy, letting some of the cum drip out as well.

“turn over.”

You rolled over to your front and Blue lifted your hips so your ass was in the air. You pressed your head down further into the mattress. Blue dragged the tip of his cock along your puffy folds. 

“you’ve let so much spill out of you already,” Blue said. Without warning, he entered you again and began to thrust at an unforgiving pace. “i thought you said you could handle it. that you wanted it all?” He started playing with your clit again, rubbing quickly to try and bring you to a second orgasm.

You moaned against the pillow. “I do. I want you so badly.”

“i want to fuck you all night long, to pound into you until you can’t walk anymore.”

“Please,” you whined.

“you’re all mine. this shows you’re all mine. you’re gonna smell like me for weeks after this. i want to cum into you…i…i want to cum into you so much i breed you.”

You craned your neck ever so slightly so that you could see the look on Blue’s face. His cheekbones were a nice, dark navy. Breeding, huh? You smiled to yourself before turning your head back.

“Then do it,” you said. “Cum into me so much you breed me.”

Blue leaned so he was resting on your back as he rut into you. He brushed a lock of hair out of the way and whispered into your ear, “yeah, you’d love that, huh? you’d love to carry my children. to hold all my seed in you until you have a baby. tell me how much you love my cum coating your insides.”

“God, I love it. Your cum feels so good in me, Blue.”

Blue let out a high-pitched whine as he pumped in another hot load. He continued thrusting into you from behind. “you’re going to take so much more of me in, even if i have to make more room,” he said, and you felt his dick twitch before slowly swelling a bit, delightfully stretching you open. 

Once again, the sensations began to overwhelm you and you panted as Blue refused to slow down. You moaned and swore as you convulsed around his cock a second time. He continued to massage your clit, forcibly eliciting a third orgasm.

“you’re gonna make such a good mom. how many children are you gonna bear me? how many babies can i fit into your womb?”

“How…how many you want?” you asked breathlessly. “How many skeleton babies do you want to put in my belly _daddy_?”

“f-fuck.” Blue pulled your hips into him as he spasmed. More and more cum dripped down your legs, pooling into the bed sheets.

“You know, this context isn’t what I pictured when I imagined calling you daddy in bed.”

Blue huffed, though you could tell he was stifling a laugh, and gripped your ass tighter. “if you’re still talking, i haven’t fucked you hard enough yet.”

“Hm, if I’m still talking you should figure out someway to keep me quiet,” you said, propping yourself up onto your elbows. You bit your lip suggestively.

Blue removed himself from you and your knees buckled. You rolled over and tried to sit up so you could kneel for him, but Blue pushed you forcefully back into the mattress. “i don’t want you to lose another drop,” he said. He grabbed your arms and dragged your upper torso to the edge of the bed. Your head hung slightly off the edge. Blue hopped off the mattress, standing in front of you, positioning his cock to enter your mouth.

It was much bigger than it usually was, and you were eager to let him facefuck you with it. He grazed your lips, wetting them with a mix of his cum and your fluids before shoving himself in your mouth.

Your tongue lapped at the underside of his dick before swirling your tongue around the tip. This position made it harder for you to bob your head, so you moved very slowly up and down his shaft. 

“deeper,” Blue said, grabbing your cheeks and pushing his cock down your throat. He pulled back out and rammed in again, forcing you to take its entire length. You reached out to grab ahold of his femurs to keep yourself steady as he started picking up the pace. 

You did your best to keep your cheeks sucked in and taut, keeping your mouth tight as you were running your tongue along him. 

“so wet. so tight. so warm,” Blue mumbled to himself as he dug his nails into your cheeks.

You hummed around his girth and Blue shrieked a string of curse words. Hot liquid poured down your throat but there was just _so much_. It filled your mouth, pooling in your cheeks even as you tried to swallow it. 

You did your best to suck off all the excess and swallow it before Blue removed himself from your mouth. You reached up with one of your hands to stroke him. “How are you doing sugar skull?” you asked. 

Blue calmly pet the side of your head. He was shaking with a soft _clack-clack-clack_. You couldn’t see his face, so you delicately used your thumb to rub circles into his femur. You pumped his cock harder, focusing on the head and trying your best to match the quick pace he had been setting. Blue rocked his hips in a steady rhythm to keep up with your motions.

He was mewling now. This was probably the least energetic he had been all day. You used feather light touches on his bones, letting your hand travel up and down his thigh before settling on the ticklish spot behind his knee.

“mweh-heh-heheheheh,” he giggled. “s-stop that! that tickles!”

“I know,” you teased, mercilessly tickling him as you stroked.

“i mweh-heheheh, i strongly advise you mweh, stop heheh.”

You could listen to his cute baritone laugh for hours. “Nah.”

“n-n-no! mweh-heheheh, mw-mweh! you! you’re being so mean!”

“Aw, come on Blue, you know I love you.”

“haah-!” he squeaked, cumming again, spurting out all over your chest.

For a moment, the room was quiet.

You had never said that before. You didn’t really mean to say it. Not because you didn’t mean it, but it just didn’t seem like this was the most opportune time for it to…come out.

Blue gently guided your head back up and helped you sit up. His eye lights were big as saucers, shaped into hearts. He broke into a big smile and grabbed your legs to shift your position. Your head hit the pillow and Blue was on top of you.

“say it again.”

“I…I love you.”

“don’t hesitate!”

“I love you.”

He leaned down to kiss your neck. “again,” he said, nipping into the soft flesh.

“I love you.”

He reached down to spread your lips. “again.”

“I love you.”

Blue pushed into you again, slowly this time, giving you the time to adjust to him before he started rocking back and forth. “you…” he paused, rolling his hips into you. “i need you.” _thrust_ “i want you.” _thrust_ “please.”

“please,” he said again, voice hoarse. “please touch me. i need you to make me feel good. i need this. say it again. scream it for me!”

“I love you!”

_thrust-thrust-thrust_

“louder!”

“I love you!!!”

Blue swelled up a little bit more inside you, stretching you further. You moaned loudly, gripping onto his ribs. 

“t-take it! if you love me you will!” Blue said, “say it! say you love me and you’ll take it!”

“God! Yes Blue, I love you, and I will take all of you, always!”

You could feel him getting bigger every time he pulled out just to fill you again. It stung a little, but the tears in Blue’s eyes and big smile on his face more than made up for it. He thrust into you, bottoming out each time. He brushed some of your hair out of your face.

“please say it again.”

“I love you, Blue.”

His hand roamed from your face to your belly. “you’re already so full of my magic. you’re beautiful like this. mine.”

“Yours, always.”

Heat or not, you could tell how much Blue loved you by how he was looking at you right now. You committed his face to memory. All his features softened and he looked at you as though you were the only person in the entire universe worth looking at. You hoped he knew the sentiment was the same.

“never mate with anyone else. you're just mine. i can’t stand someone else seeing you like this.”

“Only you, Sugar Skull,” you promised.

“thank you for choosing me. for being with me and not my brother. for being my mate. for having my heart. please stay with me. stay forever. mother my children. be by my side. always. always. i love you,” he begged as he punctuated each sentence with deeper and deeper thrusts.

You clung to Blue as tightly as you could, relishing in this moment. You moaned and hung onto him even tighter.

“i love you so much,” Blue said, “tell me again.”

“I love you,” you whispered.

Blue’s breath hitched as he came into you again. He collapsed on top of you, crying happy tears as he told you how much he loved you. 

Monster heat, you’ve deducted, was a strange experience, but you hadn’t ever felt this much love and adoration from anyone before. You were glad that you decided to come over. You pet the top of Blue’s skull and in seconds, he was ready for another round. You smiled as he flipped you over again and started whispering about mating you.

You hoped that this week would be just as _fulfilling_ as this last hour had been.

\--

When Kiwi came home at the end of the week, you made sure to act _super_ normal as you ate your pancakes. Blue was busy making a fuss about the laundry (apparently, his bro is a neat freak or something), so you were alone in the kitchen when he finally sauntered in.

“Hey man, what’s up?”

“I See You Chose To Ignore Me.”

You shrugged. “I dunno what you’re talking about. I always listen to you…dude.”

“You Have A Hickey The Size Of China On Your Neck…And Some Of My Bro’s Jizz Running Down Your Leg.”

“Wh-what?!” you looked down…and saw nothing.

“Gotcha,” he said. Kiwi grabbed an apple from the fruit bowl. “But, Yanno, You Wouldn’t Have Fallen For My Jape If You Hadn’t Been Here.” He bit into the fruit with a loud _crunch_ as he walked past you towards his room. “Later.”


End file.
